Dtr offset master and composition for preparation of same

ABSTRACT

An offset master adapted to be imaged to provide an ink receptive oleophilic image by diffusion transfer from an exposed silver halide negative in which the offset master is formed of a base sheet having a water soluble, water receptive, hydrophilic lithographic surface on which the image is deposited and which includes the combination on the lithographic surface of a nucleating agent for silver halide, a sensitizing dyestuff which renders more hydrophobic and ink receptive the silver image that is formed by reduction of silver halide on the lithographic surface of the master and a water soluble salt selected from the group consisting of zirconium, thorium and titanium, and which may include a cadmium salt in addition to the zirconium, thorium or titanium salt.

I United States Patent 1111 3,552,316

72 Inventor Mary K. Ormsbee 3,309,990 3/1967 Klupfel etal. 101/456 River r 1 3,31 1,473 3/1967 Foster et a1. 96/29 [21] App1. No. 527,028 FOREIGN PATENTS 1 1 Filed Feb-14,1966 202,937 12/1954 Australia 96/29 1 1 s- Jan-5,1971 830,623 3/1960 Great Britain... 101/1492 Asslsnee Dick 12 856,770 12/1960 Great Britain... 101/1492 1 Niles, Ill. 1 1 565,696 7/1960 Belgium 96/29 a corporation of Illinois Primary Examiner-George F. Lesmes Assistant Examiner-J. P. Brammer [54] DTR OFFSET MASTER AND COMPOSITION FOR Attorney-McDougall, Hersh & Scott PREPARATION OF SAME 9 Claims, 3 Drawing Figs.

[52] n 101/4591 ABSTRACT: An offset master adapted to be imaged to pro- 101/462,96/29, 6/ vide an ink receptive oleophilic image by diffusion transfer [51] InLCl B4ln 1/04, from an exposed silver halide negative in which the offset 1/ l 5/ 54 master is formed of a base sheet having a water soluble, water [50] Field ofsearch 96/29, 76; receptive hydrophihc lithographic surface on which the 101/149, 2, 456, 466, 453, 459, 462 image is deposited and which includes the combination on the lithographic surface of a nucleating agent for silver halide, a [56] References Cited sensitizing dyestuff which renders more hydrophobic and ink UNITED STATES PATENTS receptive the silver image that is formed by reduction of silver 2,352,014 6/1944 Rott 96/29 halide on the lithographic surface of the master and a water 2,814,988 12/1957 Bradstreet et al.. 101/466 soluble salt selected from the group consisting of zirconium, 3,169,065 2/1965 Sorkin et a1 101/456 thorium and titanium, and which may include a cadmium salt 3,220,837 1 1/1965 Land et al 96/29 in addition to the zirconium, thorium or titanium salt.

1 d is a o DTR OFFSET MASTER AND COMPOSITION FOR PREPARATION OF SAME This invention relates to the art of offset or lithographic duplication and more particularly to a new and improved offset master and method for the preparation of same.

Offset masters for offset copy work are generally of the direct image type wherein the hydrophilic lithographic surface of the master is imaged directly by the application of an oleophilic ink receptive imaging material, as by inscribing with a crayon or ink, or by transfer from a carbon sheet in response to compression or impact by stylus, typewriter key, die impression or the like. When mounted on a lithographic press and wet with an oleophilic ink composition and an aqueous repellent, the non imaged portions of the master accept the aqueous repellent while the ink composition is takenupby the oleophilic ink receptive imaged portions of the master for subsequent transfer either directly to copy sheets brought into surface contact with the inked master or indirectly to an offset blanket from which the image is transferred to copy sheets.

When it is desirable to prepare an offset master imaged from an original, it has been necessary to make'use of an indirect offset master, more often referred to as a photolithographic master. A master of the type described has been produced wherein the hydrophilic lithographic surface is overcoated with a water soluble, resin forming, light sensitive diazo compound in which a negative transparency is first formed of the original and then the diazo light sensitive coating is exposed to.the developed negative transparency to resinify the diazo compound in the exposed areas while the portions of the light sensitive diazo coating in the unexposed areas are removed by washing to produce an imaged photolithographic plate. Others of the photolithographic masters are somewhat similar in construction in that the master sheet is presensitized with a light sensitive material that is convertible to an ink receptive imaging material upon exposure to light. Such presensitized photolithographic masters are subject to a number of deficiencies including high cost, short shelf life, the need to make use of specialized equipment and materials, and the need to prepare a negative transparency by conventional photographic technique.

I More. recently lithographic or offset masters capable of being imaged by diffusion transfer technique from an exposed by undeveloped silver halide negative have been produced in which thehydrophilic, lithographic surface is provided with a nucleating or fogging agent for reducing silver halide to an ink receptive, water repellent silver image whereby, when the master sheet is brought into contact .with the exposed silver halide negative wet with a silver halide solvent and developer, the silver halide in the unexposed portions of the negative transfers by diffusion to the surface of the master where the silver halide or complex formed thereof is reduced to a silver, ink receptive, water repellent imaging material on the hydrophilic, water receptive, lithographic surface to produce the master having an image corresponding to the original.

The diffusion transfer reversal technique makes use of equipment and materials which are of low cost and which have heretofore found widespread use in single copy diffusion transferreversal processes commonly employed in the field. The diffusion transfer process also eliminates the need for the preparation of a negative transparency and the exposure of the negative transparency to a presensitized master is also completely eliminated.

It is an object of this invention to produce and to provide a method for producing a new and improved diffusion transfer reversal (DTR) offset master in which a desirable balance between the hydrophilic character of the nonimaged portion of the master and the hydrophobic character of the imaged portion of the master is improved; in which the hydrophobicity of the image formed on the lithographic surface of the master is increased; in which the image resolution is greatly improved, and wherein a large number of copies of good quality can be secured from the imaged master by conven tional lithographic duplicating technique.

These and other objects of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown'in drawing, in which: .1 y

FIG. 1 is a schematic perspective View, partiallyin section, of a DTR offset master prepared inaccordance with the practice ofthis invention; .v t 1 5 ,1. I

FIG. 2 is a schematic sectionahelevational view illustrating the process of diffusion transferto formthe image on the DTR offset master of FIG. 1; and t FIG. 3 is a perspective view par l in section of the imaged master produced in accordance wlth the practice of this invention.

The concepts of this invention reside in the fabrication of a DTR offset master formed of a base sheet 10 having a water insoluble, water receptive, hydrophilic, lithographic surface 12 which is overcoated to deposit the combination of a silver vhalide nucleating agent, sometimes referred to as a fogging agent, and oneor more metal salts which operate to enhance the formation of the silver image, its adhesion to the lithographic surface of the master, and its ink receptivity to provide a desirable balance between the hydrophilic character of the nonimaged portions and the hydrophobic character of the imaged portions whereby aqueous repellent with which the surface of the master is wet will go to the nonimaged portions, while the oleophilic inkwill wet out-the: imaged portions for the production of copy by offset onto copy'sheets.

Use can be made of a base sheet formedofafoil of an amphoteric metal, such as aluminum, copper orzinc, which the surface has been treated to render the surface hydrophilic. In the use of aluminum as the base sheet 10, thesurface can be rendered hydrophilic by brushing, orby anodizing, oriby an acid etch, and preferably by silicating, as described in the Jewett et al.U.S. Pat. No. 2,714,066. instead, use can'be-made of a coated paper master in which the base sheet' lfl isv a resinous treated, high wet strength paper which is provided with a water insoluble, water receptive, hydrophilic, lithographic coating formulated of a binder selected of a hydrophilic colloid such as casein, as in U.S. Pat. No. 2,534,650; carboxymethylcellulose, as in U.S. Pat. No. 2,542,784; alginates, as in U.S. Pat. No. 2,806,424; polyacrylates, as in U.S. Pat. No. 2,760,431; polyvinyl alcohol, as in U.S. Pat. No. 2,230,982; starch, polyvinyl acetate, and the like, with a suitable tiller such as zinc oxide, clay, satin white, and the like.

The base sheet is formed with openings 18 at the leading edge for use in mounting the imaged master onto the plate cylinder of a lithographic press but other means can be employed for engaging the leading edge of the imaged master for mounting onto the plate cylinder.

As the nucleating agent, best use is made of a stannous halide, such as stannous chloride, but other silver halide nucleating agents for the conversion of the dissolved silver halide into silver, in the absence of light, can be employed such as colloidal silver, cadmium sulfide, and the like nucleating or fogging agents described in U.S. Pat. No. 2,352,014.

It is desirable to make use of a water soluble salt of zirconium, thorium and/or titanium in combination with the silver halide nucleating agent. For this purpose, use can be made of the corresponding acetate, propionate, chloride, bromide, fluoride, and nitrate of the metals.

it is important to control the amount and ratio of materials applied to the lithographic surface. For example, in the preferred combination of stannous halide and zirconium salt, it is desirable to maintain the ratio of salts to within the range of one part by weight of the stannous salt to l to. 8 parts by weight of the zirconium salt with an optimum ratio of about i to 2.5. When the describedcombination is employed, it is desirable to deposit the mixture of salts to provide a coating weight within the range of 0.1 to 4 grams per square meter of master surface and preferably 0.5 to 3 grams pe'rsqua'ie meten v I, V

The effect of the combination of the water soluble salts can be further improved by'the modification to include a-water the accompanying soluble cadmium salt. such as cadmium acetate, cadmium chloride, cadmium nitrate and the like, alone or in combination with an antioxidant, as described in my copending application Ser. No. 526,988 filed concurrently herewith, and entitled Offset Master for Imaging by Diffusion Transfer and Method of Preparation of Same."

When the three components are employed on the lithographic surface, the materials should be applied in the same coating weight in the ratio of one part by weight of the stannous salt to l to 8 parts by weight of the zirconium salt and 0.0! to 0.5 parts by weight of the cadmium salt, and preferably one part by weight of the .stannous salt to 1.7 to 3.5 parts by weight of the zirconium salt and 0.02-to 0.2 parts by weight of the cadmium salt.

It has now been found that marked improvement can be secured in the hydrophobic character of the image that is developed on the lithographic surface of the master when the composition applied to the lithographicsurface is formulated also to contain a sensitizing dyestuff which enhances the formation of a very dense image made up of molecules which are highly hydrophobic in nature from the materials transferred by diffusion from the unexposed portions of a silver halide negative. This phenomenon is exhibited in the system described by phthalein dyes and others such as erythrosine, Eosin OJ, Eosin Y, Rose Bengal, Rhodamine dyes, and the like.

The desired novel effect is secured when the dyestuff is present in the composition in an amount, based upon the coating solids, within the range of 0.001 to 1.0 percent by weight and preferably 0.05 to 0.1 percent by weight.

The components of the overcoating may be applied from a single coating composition having a solids content within the range of 3 to percent by weight or they may be applied from separate coatings containing the ingredients in various possible combinations.

The following will illustrate the preparation of a DTR offset master embodying the features of this invention:

Example 1 Solution of zirconium acetate (13% as ZrO ml 20 Distilled water -ml- 80 Stannous chloride -g- 2 Cadmium nitrate g 0. 02 Hydroquinone monomethyl ether g 2 1% solution of Rhodamine B m1 5 Example 2 Solution of zirconium acetate (13% as ZrO m 40 Stannous chloride g 4 Distilled water -g- 160 Cadmium nitrate -g- 04 Hydr uinone monomethyl ether g 4 Eosin J g 01 Sodium sulfide -g- 05 Silver nitrate -g- 002 Example 3 Solution of zirconium acetate (13% as ZrO 20 Stannous chloride g- 3 Distilled water g- 80 Eosin OJ g- .20

} Example 4 13% solution of zirconium chloride ml, 20 Distilled water -ml- 8O Stannous acetate -g- 2 Antioxidant g 2 Erythrosine g- 01 An aluminum base sheet 10 having a silicated, water receptive lithographic surface 12 is roller coated with the compositions of examples I to 4 to provide a coating weight of about .75 gram per square meter. Theapplied coating 14 is either air dried or drying can be accelerated by heating to an elevated temperature of about l00200 F. to produce a finished master. In the preparation of a coated paper lithographic master, use is made of a coated paper direct image master formed of a high wet strength paper base sheet 10 having a lithographic coating 12 formed thereon as by a hydrophilic colloid and filler, such as described in the aforementioned patents. The lithographic surface of the coated paper base sheet is overcoated with a composition of one of the examples 1 to 4 applied in an amount to provide a dry coating weight of 0.5 to 3 grams per square meter.

In use of an offset master prepared in accordance with the practice of this invention, use is made of a negative 20 in the form of a base sheet 22 having a light sensitive silver halidegelatin stratum 24. Representative of suitable negatives are Gevaert GS negative of Gevaert Photo Production of Antwerp, Belgium, and Anken Contact Negative of the Anken Chemical Company in the United States. The negative 20 is first exposed to the original in a conventional photographic exposure apparatus. The exposed negative is then brought into pressure contact with the coated surface 14 of the master after one or both of the surfaces has been wet with a monobath developer, as represented by the following example 5:

Example 5 Parts Water 81 5 Phenidone 2. 5 Anhydrous sodium sulfite 114 Hydroquinone 24 Sodium hydroxide 24 Sodium thiosulfate 9. 8 Potassium bromide 1. 6 Carboxymethylcellulose 8. 0

For this purpose, the exposed negative and master cam be processed through an A. B. Dick Photocopier containing the monobath solution. In operation, the monobath operates to form a soluble complex of silver halide in the unexposed portions of the negative for transfer of the silver halide by diffusion to the corresponding surface of the master where the silver halide is reduced by the materials present on the lithographic surface of the master to deposit the dense masses of silver 30 concentrated at the surface of the master, to form a highly hydrophobic, ink receptive image 32 on the lithographic hydrophilic surface.

The imaged master can then be swabbed, wet or otherwise washed with a conventional fixer or conditioner, such as the CT Offset Fixer of Eastman-Kodak, or 084-4966 A. B. Dick Photoplax Conditioner, which operates to make the nonimaged areas hydrophilic and to fix the image onto the master. Thereafter the imaged master can be mounted on the plate cylinder of a conventional lithographic press for sequential wetting with aqueous repellent and oleophilic ink composition whereby the nonimaged portions of the plate are wet by the repellent while the imaged portions receive ink whereby thousands of copies of good quality can be produced.

By way of modification, instead of procurement of an image having greater hydrophobicity by the incorporation by a dyestuff of the type described into the overcoating, the hydrophobic character of the formed can be greatly improved by the formulation of the coating composition to include an additional amount of silver salts as additional nucleating agent. While such silver salts are not in any way equivalent to the dyestuffs, such additional nucleating agents can be incorporated without the dyestuff to give the desired result but it is preferred to make use of such additional amounts of silver salts in combination with the dyestuff of the type heretofore described. For such silver compounds which are employed as additional nucleating agent in the coating, use can be made of silver acetate, silver nitrate, silver sulfide and the like, as represented by the following examples:

. Example 6 Solution of zirconium acetate (13% as ZrO ml- 2O Distilled water ml 80 1.3% solution of silver acetate -ml 40 Stannous chloride g 2 Example 7 Mixture A:

22% solution of zirconium chloride ml 20 6% solution of acetic acid ml 15 Stannous chloride g 2 Distilled water -ml- 80 2% solution of cadmium nitrateml 1 Mixture B:

Mixture A -ml- 30 .5% solution of sodium sulfide- -ml- 1 .5% solution of silver nitrate m1 1. 5 Peregal (General Aniline & Film Co.) 0

The composition of example 6 or mixture B of example 7 can be coated onto the lithographic surface of an offset master in the manner and amounts previously described in examples 1 to 4.

The master prepared of the compositions of examples 6 and 7 can be imaged and used in the production of multiple copies by the procedures previously described in connection with the masters produced by the compositions of examples 1 to 4.

With masters of the type embodying the features of this invention, the image that is formed by diffusion transfer from an exposed negative will remain strongly bonded to the lithographic surface so that a large number of copies of good quality can be produced by conventional lithographic duplication technique.

It will be understood that changes may be made in the details of formulation, method of application and use, without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. An offset master for imaging to provide an ink receptive oleophilic image by diffusion transfer from an exposed silver halide negative comprising a base sheet having a water insoluble, water receptive, hydrophilic lithographic surface, said master having on the lithographic surface the combination of a nucleating agent for silver halide, and a dyestuff which densifies and renders more hydrophobic and ink receptive the silver image that is formed by reduction of silver halide on the lithographic surface of the master and present in an amount within the range of 0.001 to 1.0 percent by weight of the total solids and a water soluble salt of a metal selected from the group consisting of zirconium in the absence of a cadmium salt or zirconium, thorium and titanium when a cadmium salt is also present, and in which such water soluble salt is present as a component separate and apart from the nucleating agent and in an amount within the range of l to 8 parts by weight of the metal salt per one part byweight nucleating agent.

2. An offset master as claimed incl aim 1 in which the silver halide nucleating agent is stannous halide.

3. An offset master as claimed in claim 2 in which the materials are present in the ratio of one part by weight of stannous halide, l to 2.5 parts by weight of the salt, and in which the dyestuff is present in an amount within the range of 0.05 to 0.1 percent by weight.

4. An offset master as claimed in claim 1 in which the dyestuff is selected from the group consisting of a phthalein dye, erythrosine dye, Eosin dye, Rose Bengal, and a Rhodamine due.

5. An offset master as claimed in claim 1 in which the composition on the lithographic surface contains in addition a water soluble cadmium salt.

6. An offset master as claimed in claim 5 in which the materials are present in the ratio of one part by weight nucleating agent, 1 to 8 parts by weight of the metal salt, and 0.0] and 0.5 parts by weight of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.001

' to 1.0 percent by weight.

7. An offset master as claimed in claim 5 in which the silver halide nucleating agent is stannous halide and in which the materials are present in the ratio of one part by weight of stannous halide, l to 8 parts by weight of the metal salt and 0.01 to 0.5 parts by weight of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.001 to 1.0 percent by weight.

8. An offset master as claimed in claim 5 in which the silver halide nucleating agent is a stannous halide and in which the materials are present in the ratio of one part by weight of stannous halide, 1 to 2.5 parts by weight of the metal salt, 0.02 to 0.2 parts by weight of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.05 to 0.1 percent by weight.

9. An offset master as claimed in claim 5 in which the materials are present in separate coatings. 

2. An offset master as claimed in claim 1 in which the silver halide nucleating agent is stannous halide.
 3. An offset master as claimed in claim 2 in which the materials are present in the ratio of one part by weight of stannous halide, 1 to 2.5 parts by weight of the salt, and in which the dyestuff is present in an amount within the range of 0.05 to 0.1 percent by weight.
 4. An offset master as claimed in claim 1 in which the dyestuff is selected from the group consisting of a phthalein dye, erythrosine dye, Eosin dye, Rose Bengal, and a Rhodamine due.
 5. An offset master as claimed in claim 1 in which the composition on the lithographic surface contains in addition a water soluble cadmium salt.
 6. An offset master as claimed in claim 5 in which the materials are present in the ratio of one part by weight nucleating agent, 1 to 8 parts by weight of the metal salt, and 0.01 and 0.5 parts by weight of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.001 to 1.0 percent by weight.
 7. An offset master as claimed in claim 5 in which the silver halide nucleating agent is stannous halide and in which the materials are present in the ratio of one part by weight of stannous halide, 1 to 8 parts by weight of the metal salt and 0.01 to 0.5 parts by weight of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.001 to 1.0 percent by weight.
 8. An offset master as claimed in claim 5 in which the silver halide nucleating agent is a stannous halide and in which the materials are present in the ratio of one part by weight of stannous halide, 1 to 2.5 parts by weight of the metal salt, 0.02 to 0.2 parts by weIght of the cadmium salt, and in which the dyestuff is present in an amount within the range of 0.05 to 0.1 percent by weight.
 9. An offset master as claimed in claim 5 in which the materials are present in separate coatings. 